Thermoeconomic optimization procedure is applied using genetic algorithm method to an integrated system composed of an alkaline water electrolysis unit for hydrogen production and a combined flash binary geothermal power plant for providing power input to the electrolysis unit. The objective is to minimize the unit costs of the products (electricity and hydrogen production) of the composed system. The optimization approach is developed based on the cost optimal exergetic efficiency that is obtained for a component isolated from the remaining of the system components. Objectives to be optimized given certain constraints and variables are developed for each subcomponent of the system. Using genetic algorithm method of optimization, the variables, relative cost differences, and exergetic efficiencies with the corresponding optimal values are obtained. Thermoeconomic optimal values for product cost flow rate, fuel cost flow rate, unit cost of electricity, and unit cost of hydrogen production are calculated to be 2412 $/h, 289.4 $/h, 0.01066 $/kWh, and 1.088 $/kg, respectively, whereas the corresponding actual base case values are 2607 $/h, 295.9 $/h, 0.01105 $/kWh, and 1.149 $/kg, respectively. (C) 2016 Elsevier Ltd. All rights reserved.